ach·a·la·sia \ˌakəˈlāzh(ē)ə\noun (-s) Etymology: New Latin, from a- (II)+ Greek chalasis loosening, relaxation (from chalan to loosen + -sis) + New Latin -ia : failure of a ring of muscle (as a sphincter) to relax < achalasia of the esophagus > < achalasia of the anal sphincter >